The embodiments of the invention relate generally to the packaging of integrated circuits (ICs); more particularly, a new die attach method suitable for use in packaging IC dice are described to eliminate die attach materials and reduce the cost, while providing good thermal performance and without the concern of resin bleed-out.
There are a number of conventional processes for packaging integrated circuit (IC) dice. By way of example, many IC packages utilize a metallic lead frame. The lead frame typically includes a plurality of leads or contacts, and optionally a die attach pad (paddle) upon which a die may be attached by means of a suitable adhesive material. The die is typically electrically connected to the lead frame leads by appropriate connectors such as bonding wires. In general, the die and portions of the lead frame are encapsulated with a molding material to protect the electrical connections and the delicate electrical components on the active side of the die.
The above-mentioned adhesive material can be in the format of paste (called die attach paste) or film (die attach film). Die attach paste, typically contains about 80 wt % silver filler and about 20 wt % polymer resin and additives. There are many limitations with die attach paste including resin bleed out (RBO), inconsistent die attach thickness, outgassing of organic components onto the bond pad on die surface causing non-stick on pad (NSOP) or causing the corrosion, and so on. Die attach film (DAF) has been developed to address some of the problems such as RBO and inconsistent die attach thickness. However, there are still some problems associated DAF such as limited thermal conductivity, sawing and die pickup issues. Moreover, the cost of DAF material is much higher than die attach paste.
On the other hand, much effort has been focused on gecko-inspired adhesives, which primarily rely on Van der Waals forces for adhesion by growing nanomaterials (such as carbon nanotubes) on the backside of the wafer or the chip. The growth temperature is about 750-850° C. However microelectronic chips cannot withstand so high temperature.
In view of the foregoing, there is continuing effort to produce cost effective packaging methods that provide high thermal performance at the interface of die to lead frame when implemented in molded packages.